1. Field of Invention
The present invention relates to valve stem seal assemblies adapted to be installed over valve stems that are reciprocally movable within valve guides of internal combustion engines. More particularly, the invention relates to seal assembly retainers incorporating specially designed retention mechanisms for securement of such assemblies to valve guides.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves, supported for reciprocal motion within valve guides, typically include integral elongated stems extending away from the engine cylinder heads, the ends of the stems interacting with rotating overhead cams for cyclic or repeated opening and closure of the valves against the force of valve return springs during the combustion cycle.
Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem. A plurality of valve stems move reciprocally to and from the cylinder head, each within its individual guide, and so-called valve stem seal assemblies are used to seal against leakage of oil through a mechanical clearance path between each annular engine valve guide and its associated valve stem.
As is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotatable with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, most internal combustion engines have at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of similar construction, and both include stems integrally affixed to the valves.
In the typical engine, a valve stem seal assembly is fitted over or atop each valve guide, wherein each seal assembly includes a retainer frictionally mounted to an associated valve guide. Each valve stem seal assembly normally has two primary parts: 1) an elastomeric oil seal for controlling leakage of oil between the valve stem and guide as noted, and 2) a structural cylindrical retainer mounted atop of the valve guide to hold the oil seal in place.
Although valve stem seal elastomer body design, performance, and construction issues have seen much progress in recent years, there are current incentives to reduce manufacturing costs, particularly costs associated with the structural cylindrical retainers.
The valve stem seal retainer of the present invention addresses the noted manufacturing cost issues by providing a cost-effective, yet field flexible, design to accommodate a wide variety of valve guide geometries. Moreover, the structure is easily tailored to provide for proper retention of a valve stem seal assembly to a valve guide under a variety of installation and retention load requirements.
The disclosed invention is a one-piece valve stem seal and retainer assembly for an internal combustion engine. A plurality of such assemblies is contemplated for use in an engine, each designed for insertion over an engine valve guide for continuous engagement with an associated reciprocally moveable valve stem. The valve stem seal includes a retainer having a completely cylindrical, i.e. straight walled, metallic body. The body defines an interior surface to which an elastomeric sealing element is chemically bonded to provide a one-piece structure. The retainer is adapted to be inserted atop of an upper smaller diameter portion of a valve guide. It is inserted down over the guide to a point where it bottoms against a step formed between the upper smaller diameter portion and a lower larger diameter portion of the guide. The retainer is sized so as to provide a diametric offset with respect to the larger diameter portion of the guide; the offset provides a mechanism for avoiding interference between a valve return spring and the exterior retainer body. An upper section of the elastomeric sealing element contains a pair of sealing lips, including an oil sealing lip and a gas sealing lip. The upper portion of the sealing element also provides metering of a small amount of oil through the interface between the seal and associated valve stem for assuring adequate lubrication of the stem and guide interface.
A lower portion of the elastomeric sealing element includes one or more annular gripping ribs that engage the guide via interference fit to assure requisite valve stem seal retention force on the guide. Such force is sufficient to overcome countervailing forces tending to remove the seal from the guide that are created by reciprocal movement of the valve stem through the sealing lips. To the extent that the metallic retainer extends fully to the upper extremity of the elastomeric sealing element, the seal may be installed with a hammer, or other flat-faced tool, thus eliminating need for use of any special tool for its installation on a valve guide.